It is desirous to have lightweight structures that have a high degree of thermal insulation that can be washed and dried without retention of a great amount of water. Fiberglass containing structures are presently being used to provide fiber battings for use in insulating spaces in buildings and airplanes. In addition, fiberglass battings are being used as insulation in industrial apparel, blankets and curtains.
The problems with fiberglass is that it is difficult to handle and can cause dermal invitation. Moreover, fiberglass does not have a high insulation compact value and can pick up moisture so as to cause it to settle down after installation with a loss in insulation value.
Styrenic fibers are well-known. Moreover, styrenic fibers are low in cost, are non-irritating, have good insulation value and can be blended with other fibers utilizing conventional processes. The main disadvantage of styrenic fibers is that they are highly flammable. Hollow styrenic fibers are even more flammable because they provide a greater surface area for combustion.
Hollow fibers can also be prepared from other thermoplastic materials which have better fire resistant characteristics than styrene. However, the fire resistance of these thermoplastic materials also decreases when formulated into hollow fibers.
It is now known that carbonaceous fibers can provide a synergistic improvement in fire resistance when blended with flammable materials.
U.S. Pat. No. 4,837,076, to McCullough, Jr. et al, which is herein incorporated by reference, relates to the preparation of non-linear carbonaceous polymeric fibers and to carbonaceous polymeric fibers having different electroconductivity. This patent discloses a process which can be used to heat treat and carbonize expanded polymeric fibers to yield the fibers of the invention.
U.S. Pat. No. 4,898,783, to McCullough Jr. et al, which is herein incorporated by reference, discloses the synergism found with a blend of solid carbonaceous polymeric fibers and solid thermoplastic fibers.
U.S. Pat. No. 4,752,514, to Windley, which is herein incorporated by reference, discloses crimped and expanded polyamide fibers. The crimps in the fiber are caused by collapsed portions. There is also disclosed a process for preparing precursor fibers useful in the present invention.
U.S. Pat. No. 4,877,093, to Murata et al, which is herein incorporated by reference, discloses porous expanded acrylonitrile based fibers and a process for their preparation. The process can be used for preparing one of the precursor fibers of the invention.
U.S. Pat. No. 4,832,881, to Arnold Jr. et al, discloses the preparation of low density, microcellular carbon foams from polyamides, cellulose polymers, polyacrylonitrile, etc. The foams are rigid and brittle.
For the purpose of rendering various terms employed herein clear and readily understandable, the following definitions are provided hereinafter.
The term "stabilized" herein applies to fibers which have been oxidized at a specific temperature, typically less than about 250.degree. C. for acrylic fibers. It will be understood that in some instances the fibers are oxidized by chemical oxidants at lower temperatures. The procedure is more clearly described in U.S. Pat. No. 4,837,076, which is herein incorporated by reference.
The term "reversible deflection" as used herein applies to a helical or sinusoidal compression spring. Particular reference is made to the publication, "Mechanical Design--Theory and Practice," MacMillan Publishing Co., 1975, pp 748, particularly Section 14-2, pp 721 to 724 as well as the herein before mentioned European published Application serial number 0199567.
The term "polymer" or "polymeric material" used herein applies to organic polymers as defined in Hawley's Condensed Chemical Dictionary, Eleventh Edition, Published by Van Nostrand Rheinhold Company. The organic polymers generally include: 1) natural polymers, such as cellulose, and the like; 2) synthetic polymers, such as thermoplastic or thermosetting elastomers; and 3) semisynthetic cellulosics. Polymers included herein are also low melting polymeric binders as well as polymeric fibers.
The term "carbonaceous fibers" as used herein is intended to include linear or nonlinear carbonaceous fibers, or mixtures of such fibers.
The term "carbonaceous fiber structure" as used herein relates to polymeric fibers whose carbon content has been irreversibly increased as a result of a chemical reaction such as a heat treatment, as disclosed in U.S. Pat. No. 4,837,076, and is at least 65%.
The term "nongraphitic" as used herein relates to those carbonaceous materials which are substantially free or oriented carbon or graphite microcrystals of a three dimensional order, typically have an elemental carbon content less than 98% and as further defined in U.S. Pat. No. 4,005,183.
The term "ignition resistant" as used herein generally applies to any one of the characteristics that are referred to as flame arresting, flame retarding, fire shielding and fire barrier, as defined in 14 CFR 25.853(b).
An article is considered to be "flame retarding" to the extent that once an igniting flame has ceased to contact unburned parts of a textile article, the article has the inherent ability to resist further propagation of the flame along its unburned portion, thereby stopping the internal burning process. Recognized tests to determine whether an article is flame retarding are, inter alia, the American Association of Textile Chemists and Colorist Test Method 34-1966 and the National Bureau of Standards described in DOC FF 3-71.
An article is considered to be "flame arresting" if it has the ability to block or prevent flames from contacting unburned parts of a flammable substance at least five (5) minutes.
An article is considered to be "fire shielding" if it is capable of deflecting flames and the radiation therefrom in a similar manner as aluminum coated protective garments, which are known in the art.
Fire barriers have the characteristic of being nonflammable and flame retarding and also provide thermal insulation characteristics.
The term "polymeric" or "polymeric resin" used herein includes natural polymers as well as other organic polymeric resins including organosilicone polymers.
The nonlinear carbonaceous fibers preferably used in the invention are resilient, shape reforming and have a reversible deflection greater than about 1.2:1. It should be understood that the reversible fiber defection comprises two components, pseudoelongation and fiber elongation. Pseudoelongation results from the nonlinear configuration and/or false twist imposed on the fiber. Fiber elongation is the elongation to fiber break after the fiber has been made linear.
The carbonaceous materials that are suitably employed in the present invention have an LOI value of greater than 40 as measured according to test method ASTM D 2863-77. The method is also known as the "oxygen index" or "limiting oxygen index" (LOI) test. With this procedure the concentration of oxygen in O.sub.2 /N.sub.2 mixtures is determined at which a vertically mounted specimen is ignited at its lower end and just continues to burn. The size of the specimen is 0.65.times.0.3 cm with a length of from 7 to 15 cm.
The LOI values of different materials are calculated according to the following equation: ##EQU1##
The carbonaceous materials of the invention are characterized as having a percentage value greater than 65 and thermal conductivity of less than 1 BTU ft/hr ft.sup.2 .degree.F. The percent char formation and thermal conductivity of various other materials are as follows:
______________________________________ Thermal % Char Conductivity ______________________________________ Carbonaceous particles 18.6% N.sub.2 &gt;65 0.1 16.0% N.sub.2 &gt;65 0.2 KEVLAR 60 &lt;1.0 KODEL 410 polyester 10 &lt;1.0 Polyacrylonitrile 60 &lt;1.0 Oxidized polyacrylonitrile 60 &lt;1.0 THORNEL 300* &gt;95 4.84 Cotton &gt;30 &lt;1.0 Rayon &lt;50 &lt;1.0 Polycarbonate 22 &lt;1.0 Polyethylene terephthalate 10 &lt;1.0 Carbon particles &gt;90 2.5 THORNEL P758** &gt;95 106.48 ______________________________________ *Trademark of Amoco Corp., Danbury, CT, for graphite yarn **Trademark of Amoco Corp., Danbury, CT, for graphite yarn derived from pitch.
The measurement of char formation as illustrated in the aforementioned table and as discussed herein is made by using a standard thermogravimetric analysis apparatus that is adapted to perform the analysis in a nitrogen atmosphere. The apparatus is described in Encyclopedia of Polymer Science, Vol. 14, p. 21, John Wiley & Son, 1971.
The measurement is performed by loading a sample onto a sample pan of the thermogravimetric analysis apparatus. The sample is then heated in an nitrogen atmosphere at a rate of 10.degree. C./min from ambient temperature to 900.degree. C. The thermogravimetric apparatus records the sample weight remaining versus temperature. The percent of original weight remaining at 800.degree. C. is taken as the char percentage.